There has recently been a demand for converting a serial signal conforming to the USB (Universal Serial Bus) 3.0 standards (hereinafter, described as USB 3.0 signal) into an optical signal or a millimeter-wave signal and transmitting the converted signal.
In the USB 3.0, two types of signals, i.e., LFPS (Low Frequency Periodic Signaling) as low-speed control signal having a long period of 20 ns to 100 ns, and a high-speed transmission signal of 5 Gbps are transmitted. Further, in the USB 3.0, the following specifications are determined: a time period without transmission signal is set to an Electrical Idle state where no signal exists in the transmission path.
Therefore, in order to achieve the demand described above, it is desirable to make it possible to receive a serial signal including a plurality of signals having different speeds, i.e., a low-speed control signal and a high-speed transmission signal, and to transmit the received serial signal with high quality to a communication apparatus at a subsequent stage, the communication apparatus performing optical communication or millimeter-wave communication.
Meanwhile, a technology capable of detecting the USB 3.0 signal with low power consumption has been proposed in the past (see, for example, Patent Literature 1).